This invention relates generally to mirror systems for vehicles and more particularly to such mirror systems having controls for adjustment of the reflectance level of one or more mirrors The invention is especially adapted to mirror systems utilizing continuously variable reflectance elements such as electrochromic elements
Automatic rearview mirrors which sense glare-producing light and ambient light conditions and which automatically control the reflectivity level of the mirror have become sophisticated in establishing an optimum reflectivity level. Examples of such systems are included in U.S. Pat. No. 4,793,690 to Edward A. Gahan et al. for a REARVIEW MIRROR CONTROL CIRCUIT, and U.S. Pat. No. 4,886,960 to Keith W. Molyneux et al. for a CONTROL CIRCUIT FOR AN AUTOMATIC REARVIEW MIRROR. Such systems typically provide a manual sensitivity adjustment The control then automatically establishes the reflectivity of the reflectance element based upon the sensed level of ambient light and glare-producing light, as well as the sensitivity level selected by the driver
While such automatic controls are very satisfactory for many automotive applications, especially for automobiles and small trucks, they are not necessarily desirable for all applications. A rearview mirror can serve two functions The first is "dimensional" in that the driver bases distance/dimension decisions on the reflected image. The second function is providing awareness to the driver of vehicles immediately adjacent in side-lanes or to the rear. In an automobile, the interior mirror, and to a lesser extent, the driver-side outside mirror, serve both the dimensional and awareness functions. The passenger-side mirror in an automobile, which is typically convex, is principally an awareness device. By contrast, the outside mirrors on large commercial vehicles, such as trucks and buses, equally function as dimensional and awareness devices. Indeed, a truck driver's skill is significantly determined by the ability to use the outside mirrors, especially for dimensional/distance decisions. Thus, automatically controlled mirrors have disadvantages for, and are somewhat disagreeable to, truck drivers who both desire and require user-control over the reflectivity of any variable reflectance mirrors mounted on their vehicle. Thus, manually controlled (otherwise known a remote-controlled or user-controlled mirrors), which provide control by the driver over the mirror reflectivity, are particularly desirable to truck drivers. The driver desires to manually select the level of reflectivity for the mirror most appropriate for the truck driving task. Such reflectivity depends on the ambient lighting conditions, on the level of both headlamp glare, and, surprisingly, sunlight glare experienced, and on whether the driver is reversing or turning a corner.
Truck drivers in particular, but all drivers in general, even by day, benefit from a variable reflectance mirror capable of high, moderate and low reflectance levels. Within this context, high reflectivity is a mirror reflectance level that approaches, as close as is practical, to the 90% (as measured using test method SAE J964a, Society of Automotive Engineers, Warrendale, Pa.), or thereabouts, which equals the reflectance level conventionally provided by second-surface silvered mirrors Car drivers, particularly in the Unite States, have for decades opted to use exterior rearview mirrors that use as their reflector element a thin film of chromium metal and achieve thereby a reflectance level of 55%+/-5%, or thereabouts, which is considered moderate in reflectance level. Such a chromium mirror offers a compromise between daytime visibility and nighttime glare protection. Truck drivers, in general, and many European car drivers, have continued to favor silvered, high reflectance exterior mirrors. They apparently do so because they particularly value the extra rear vision performance of such high reflectance mirrors and are willing to suffer the excessive glare reflected by said high reflectance mirrors. Thus, many drivers desire a high reflectance mirror with a reflectivity of at least 60% desired, and greater than 70% preferred, but with the capability to vary the reflectivity of said mirror so that a high reflectance can be selected when appropriate and a lower, dimmed reflectance can be selected when appropriate.
Large trucks typically do not have an interior mirror. While vans and other commercial vehicles may have interior mirrors, the view afforded by such interior mirrors is limited at best. Truck drivers and other professional drivers use their outside mirrors as a primary driving aid and, as such, use and depend upon their mirrors to a much greater extent than do ordinary drivers. Because of the primary importance served by the rearview mirrors to professional drivers, such drivers desire greater personal control over operation of the mirror. Mirror glare is an especially severe problem for professional drivers who drive for long periods and are more likely to be driving during nighttime hours. Furthermore, the large size of truck mirrors increases the amount of glare that may be reflected into the eyes of the driver. Such glare creates eye fatigue which adds to the overall fatigue experienced during long trips. Therefore, what may be a mere annoyance to a casual driver, may be a safety problem for the professional driver.
In addition to their use in long-haul situations, rearview mirrors for trucks play a critical role in ensuring that the driver has adequate awareness and cognizance of traffic conditions rearward and in adjacent lanes when making lane-change decisions. The field of view and clarity of image and reflectance level must be such that the driver can quickly and easily determine traffic condition in all weather conditions, day or night. The vehicle's rearview mirrors must provide an image which is bright enough for the driver to quickly and easily gather information concerning vehicles, pedestrians and cyclists even in low light level conditions. On the other hand, the mirror must not present an image that is so bright that it causes glare or produces fatigue.
When reversing into loading docks and the like, truck drivers require their mirrors for maneuvering and require a high level of reflectivity so that the driver can clearly discern what is happening on both sides of the vehicle even under severe conditions. For example, the driver may be reversing the truck from the bright outdoors to a typically darker loading dock bay. In addition to reversing into loading dock bays, truck drivers must use their rearview mirrors when making turns. Class 8 truck drivers drive vehicles making wide-angle turns and the driver must frequently use, and depend for decision making upon, the exterior rearview mirrors. Indeed, when the vehicle is equipped with more than one variable reflectance mirror, the driver may desire that only one of a particular combination of mirrors in the system rapidly return to the high reflectance state while the remainder of the mirrors continue in their dimmed state. Likewise, when turning from a heavy-traffic road onto a low-traffic road, having a lower level of ambient light, the driver may desire that, upon selection, the mirror(s) be capable of rapidly returning to the highest reflectance state achievable Whereas it may be acceptable that the mirror dim under manual control to a low reflectance state over a period as long as several tens of seconds, it is desirable that the mirror return to high reflectivity more rapidly and be accomplished in a matter of a few seconds, and preferably one to three seconds. Therefore, it is important that the time taken to return from a significantly dimmed reflectance level to a high reflectance level (which is the rate of bleaching) be rapid. Accordingly, mirror systems for large trucks must allow the driver to respond to a number of critical situations. In many such situations, speed of response is critical.
Non-professional drivers also often desire greater user control over the reflectance level of the mirrors. Remotely actuated mirrors have been provided which allow the driver to actuate a two-state, prism-type mirror between states. While such remotely actuated mirrors put control of the mirror in the hands of the driver, they do little more than duplicate the manual flipping of a conventional mechanical rearview mirror.